1. Field of the Invention
The present invention relates to an electromagnetic transducer incorporated in a magnetic recording medium drive such as a hard disk drive (HDD), a magnetic tape drive, and the like, for example. More particularly, the invention relates to a method of determining the magnitude or current value of a so-called sensing current to be supplied to an electromagnetic transducer.
2. Description of the Prior Art
When an electromagnetic transducer such as a giant magnetoresistive (GMR) element is utilized to read out magnetic information data, for example, a sensing current is supplied to the electromagnetic transducer. The inversion of the direction of an acting magnetic flux or field induces variation in the voltage appearing in the electromagnetic transducer in response to supply of the sensing current. Such variation in the voltage serves to identify the magnetic binary data. The higher the recording density is to be achieved in a magnetic recording medium such as a hard disk, a larger current value is required to the sensing current. Without the sensing current of a larger current value, it is supposedly impossible to read the magnetic information data out of the magnetic recording medium without an error.
On the other hand, a sensing current of an increased current value is supposed to induce deterioration in the electromagnetic transducer and/or to shorten the lifetime of the electromagnetic transducer. It is thus required to set the current value of the sensing current at the highest level which still ensures a longer lifetime of the electromagnetic transducer. Heretofore, no specific method of determining the magnitude of the sensing current has been proposed to meet this demand.
It is accordingly an object of the present invention to provide a method of determining the magnitude or current value of a sensing current, which is capable of setting the sensing current of a larger magnitude while satisfying the demand for a longer lifetime of an electromagnetic transducer.
According to the present invention, there is provided: a method of determining a magnitude of a sensing current to be supplied to an electromagnetic transducer, comprising: supplying an electric current of a first current value to the electromagnetic transducer; determining a physical quantity appearing in the electromagnetic transducer based on the electric current of the first current value; supplying an electric current of a second current value, different from the first current value, to the electromagnetic transducer; determining the physical quantity appearing in the electromagnetic transducer based on the electric current of the second current value; and determining the magnitude of the sensing current based on change found in the physical quantity.
If any correlation can be found between the physical quantity and the variation in temperature in the electromagnetic transducer, the variation in temperature can be determined based on the change or variation in the physical quantity. The variation in temperature can thus be determined for the specific electromagnetic transducer. If the current value for the sensing current can be determined based on the determined variation in temperature for the specific electromagnetic transducer, it is possible to set the optimal current value unique to the specific electromagnetic transducer.
As conventionally known, the lifetime of the electromagnetic transducer such as a magnetoresistive (MR) element greatly depends upon the temperature. If the variation in the temperature of the electromagnetic transducer is actually measured in determining the current value of the sensing current in the above-described manner, it is possible to reliably set the maximum current value for the specific electromagnetic transducer without suffering from deterioration or a shortened lifetime resulting from pa fracturing or destructive phenomenon such as a so-called migration. Setting of the thus determined maximum current value for the sensing current enables an accurate detection of the magnetic binary data while satisfying the demand to a longer lifetime of the individual electromagnetic transducer.
Specifically, the method of determination may further comprise: calculating a first electric resistance value of the electromagnetic transducer based on a first voltage value appearing in the electromagnetic transducer in response to supply of the electric current of the first current value; calculating a second electric resistance value of the electromagnetic transducer based on a second voltage value appearing in the electromagnetic transducer in response to supply of the electric current of the second current value; and calculating a quantity of variation in temperature of the electromagnetic transducer based on the first and second electric resistance values in determining the magnitude of the sensing current, for example.
In determining the maximum current value for the sensing current, the method of determination preferably changes the second current value so as to calculate the variation in temperature. As conventionally known, a specific correlation can be found between the lifetime of the electromagnetic transducer such as an MR element and the variation in temperature as well as the magnitude of the electric current. If the variation in temperature and the current value are revealed, it is possible to presume an expected lifetime of the electromagnetic transducer. When the thus presumed lifetime is compared with a predetermined reference or target lifetime of the electromagnetic transducer, the maximum current value for the sensing current, satisfying the demand to a longer lifetime of the electromagnetic transducer, can be obtained in a facilitated manner.
The aforementioned method of determination may be applied to a magnetic recording medium drive incorporating not only an electromagnetic transducer for reading data but also an electromagnetic transducer for writing data paired with the electromagnetic transducer for reading data. In this case, when the second electric resistance value is to be detected at the electromagnetic transducer for reading data, it is preferable that an electric current is also supplied to the electromagnetic transducer for writing data. In general, the variation in temperature of the electromagnetic transducer for writing data influences the temperature of the electromagnetic transducer for reading data in a service environment. If the electric current is supplied to the electromagnetic transducer for writing data in this manner, the second electric resistance value of the electromagnetic transducer for reading data can be detected in a condition similar to the service environment. Accordingly, the aforementioned maximum current value can be derived at a still higher accuracy.
The aforementioned method of determination can be realized with the performance of a so-called computer, a central processing unit (CPU), a microprocessor unit (MPU), and the like. In this case, a software program designed to realize the method of determination may be stored in a portable storage medium such as a diskette (FD), a compact disk (CD), a memory card, and the like, for example. Alternatively, the software program may be stored in a memory chip such as a flash memory, and the like. Such a memory chip may be mounted on a printed circuit board to be incorporated or assembled in a recording medium drive such as a hard disk drive (HDD), a magnetic tape drive, and the like.